1. Field of the Invention
The present invention relates to an electric vehicle which is driven by a motor, and more particularly, to an electric vehicle provided with a secondary battery and a generator as an energy source.
2. Description of the Prior Art
An electric vehicle is preferably used in view of air pollution, noise level and diversification of energy consumption. Such an electric vehicle is generally provided with a motor, a controller, and a battery which are used instead of an engine, a transmission, and a fuel tank in the internal combustion engine. Typical batteries for electric vehicles include a secondary battery and fuel cells, which are chemical batteries. The secondary battery is rechargeable by means that direct current energy is applied to the cells reversely as compared with the discharging condition. A fuel cell is normally operated by continuously receiving fuel gas therein and directly transforms the chemical energy of fuel gas into electric energy. Various types of fuel cells have been proposed and practically used, which include, for example, hydrogen-oxygen fuel cells, carbonate hydrogen fuel cells, hydrazine fuel cells, ammonia fuel cells, and methanol fuel cells.
Hitherto a direct-current generator was popularly used as a generator for the electric vehicle. Since the technology of the power electronics has been remarkably improved, thyristor motors and induction motors have become used as motors of an electric vehicle. Furthermore, such motors are controlled by various control methods such as a voltage changing control, a resistance control, a thyristor chopper control, a transistor chopper control, and an inverter control.
One typical electric vehicle is disclosed in FIG. 6. The electric vehicle is provided with a secondary battery 1 and a fuel cell power system 2 as an energy source. The secondary battery 1 is disposed in a lower and center portion of the vehicle so as to be rechargeable from the fuel cell power system 2 and to be dischargeable to a motor (not shown). The fuel cell power system 2 includes a stack 3 which is formed by laminating a plurality of cell units. The stack 3 receives fuel which is sent to it from a fuel reforming device 4 having a burner (not shown), and air which is heated by a heat exchanger 5 and is supplied from an air supply unit 6. The reformed fuel and the heated air chemically react in the stack 3 so that chemical energy is transformed into electric energy.
In the stack 3, it is necessary to remove the heat incurred by the reaction bared electric generation and to keep the temperature of the cells at a suitable level in order to prevent parts of the stack 3 from degrading their quality, and to equalize a reaction speed of electric generation. Therefore, a circulating pump 7 circulates a coolant to the stack 3 so that the stack 3 is kept at an optimum temperature. A chopper 9 controls an applied voltage which is supplied from the stack 3 to the motor by means that the chopper 9 speedily connects from disconnects the stack 3 and the electric source through a thyristor or transistor (not shown). With this rapid chopping operation, a current-carrying ratio (an ON-OFF period ratio per hour) is varied. Therefore, an average applying voltage is continuously varied from zero volts to the maximum value of the battery. An air conditioner 10 is disposed at a roof portion in the electric vehicle in order to control the temperature and the humidity of the passenger room.
However, the fuel cell power system 2 is continuously operated under a running condition of the electric vehicle. Accordingly, the electric vehicle normally occurs noise and exhaust gases such as CO.sub.2 under a running condition. Furthermore, since the secondary battery 1 supplies electric energy to the motor under an uphill road running or acceleration condition while the fuel cell power system 2 always produces a predetermined electric energy and supplies it to the motor, the electric vehicle encounters the difficulty that the secondary battery 1 loses its discharging ability before the fuel cell power system 2 becomes empty of fuel. This causes the problem that the electric vehicle cannot have essential vehicular performance under an uphill running or acceleration condition.